In October 2010, Labor's Mine Safety and Health Administration (MSHA) -- the Federal agency responsible for setting and enforcing mine safety and health standards -- proposed revising the existing standard for coal mine dust to lower the permissible exposure limit (PEL) from 2.0 milligrams of dust per cubic meter of air (mg/m3) to 1.0 mg/m3. Several coal mining companies and others have questioned the evidence and analytical methods used to support the proposed PEL. In the Consolidated Appropriations Act, 2012, Congress required that GAO review and report on the data collection, sampling methods, and analyses MSHA used to support its proposal. Although MSHA's proposed rule includes other provisions, this review focuses on MSHA's proposal to lower the PEL for coal mine dust from 2.0 mg/m3 to 1.0 mg/m3. To respond to this requirement, GAO addressed the following question: What are the strengths and limitations of the data and analytical methods MSHA used to support its proposal to lower the PEL for coal mine dust?
GAO's evaluation of the reports MSHA used to support its proposal and the key scientific studies on which the reports were based shows that they support the conclusion that lowering the PEL from 2.0 mg/m3 to 1.0 mg/m3 would reduce miners' risk of disease. The reports and key studies concluded that miners' cumulative exposure to coal mine dust at the current PEL over their working lives places them at an increased risk of developing CWP, progressive massive fibrosis, and decreased lung function, among other adverse health outcomes. To mitigate the limitations and biases in the data, the researchers took reasonable steps, such as using multiple x-ray specialists to reduce the risk of misclassifying disease and making adjustments to coal mine dust samples where bias was suspected. In addition to addressing the limitations and biases in the data, researchers used appropriate analytical methods to conclude that lowering the existing PEL would decrease miners' risk of developing black lung disease.
For example, GAO said that in addition to taking steps to precisely estimate a miner's cumulative exposure, the researchers accounted for several factors in their analyses -- such as the age of the miners, the carbon content of the coal (coal rank), and other factors known to be associated with the disease -- to better estimate the effect of cumulative exposure to coal mine dust. Further, the other studies GAO identified generally supported the conclusion that reducing the PEL would reduce miners' risk of disease.
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